This is just from what I've gathered. At an early point in development, the plan was to do the cutscenes in-house. That's why there's some incredibly high-poly models of characters out there. You've seen the Spartan in Kohler's gallery, but there's also another model he did of a deleted character.

: The image comes from a site called CGHUB.com, turns out its like the
: DeviantART of professional artists and modelers. and it also turns out
: theres a fuckton of 343i, certain affinity, liquid development, and Bungie
: employees here both former and current. The artist who posted this says
: its from "early development" of Wars, and since this is a site
: for professionals to dump old works I see no reason for him to lie.

Heh. It's the real deal, but sadly nothing too new.
Gene Kohler was a modeler at Ensemble Studios. He also did some concept art, but nothing that got used.

: Just thought I share, again sorry if this is slowpoke old news. :)

Hate to blow my own horn, but you might be interested in some of the other stuff that has been dug up.

http://forums.bungie.org/halo/archive35.pl?read=1041997
http://forums.bungie.org/halo/archive38.pl?read=1124014
http://forums.bungie.org/halo/archive38.pl?read=1128895
http://forums.bungie.org/halo/archive38.pl?read=1124567